linux-kernel - Re: [PATCH 1/4] zsmalloc: remove x86 dependency

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Message-ID: <4FFC4A61.3020601@linux.vnet.ibm.com>
Date:	Tue, 10 Jul 2012 10:29:37 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] zsmalloc: remove x86 dependency

On 07/09/2012 09:21 PM, Minchan Kim wrote:
> On 07/03/2012 06:15 AM, Seth Jennings wrote:
<snip>
>> +static void zs_copy_map_object(char *buf, struct page *firstpage,
>> +				int off, int size)
> 
> firstpage is rather misleading.
> As you know, we use firstpage term for real firstpage of zspage but
> in case of zs_copy_map_object, it could be a middle page of zspage.
> So I would like to use "page" instead of firstpage.

Accepted.

>> +{
>> +	struct page *pages[2];
>> +	int sizes[2];
>> +	void *addr;
>> +
>> +	pages[0] = firstpage;
>> +	pages[1] = get_next_page(firstpage);
>> +	BUG_ON(!pages[1]);
>> +
>> +	sizes[0] = PAGE_SIZE - off;
>> +	sizes[1] = size - sizes[0];
>> +
>> +	/* disable page faults to match kmap_atomic() return conditions */
>> +	pagefault_disable();
> 
> If I understand your intention correctly, you want to prevent calling
> this function on non-atomic context. Right?

This is moved to zs_map_object() in a later patch, but the
point is to provide uniform return conditions, regardless of
whether the object to be mapped is contained in a single
page or spans two pages.  kmap_atomic() disables page
faults, so I did it here to create symmetry.  The result is
that zs_map_object always returns with preemption and page
faults disabled.

Also, Greg already merged these patches so I'll have to
incorporate these changes as a separate patch.

Thanks,
Seth

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